The present invention particularly relates to a fuel injection valve used in an engine (direct injection engine) which employs a method of directly injecting fuel into a combustion chamber, among spark ignition-type internal combustion engines (gasoline engine) in which the internal combustion engines use gasoline as fuel.
In some cases, the fuel of the gasoline engine cannot be ignited when an air-fuel ratio representing a mixture ratio between air and fuel is too high or too low. In addition, if the air-fuel ratio of the air-fuel mixture is higher or lower than a theoretical air-fuel ratio, the air is oversupplied or the fuel is oversupplied. Consequently, nitrogen oxide is generated, or an unburnt fuel component (HC) is generated in some cases. Therefore, a fuel injection amount is adjusted so as to inject the fuel whose amount allows the air-fuel ratio to reach a predetermined value, thereby supplying the fuel to the combustion chamber.
In the direct injection engine, a fuel injection hole of a fuel injection valve is installed so as to be directly exposed to the combustion chamber of the engine. The fuel is sprayed and directly injected into the combustion chamber by the fuel injection valve. Timing for injecting the fuel generally falls in a range from an intake stroke to a compression stroke. Within this range, the fuel is mixed with the air so as to form the air-fuel mixture. A general port-injection engine employs a method of igniting the fuel after injecting the fuel into an intake port during an exhaust stroke and subsequently taking the air fuel mixture into the combustion chamber during the intake stroke. In contrast, the direct injection engine is different from the port-injection engine in that a time period from injection until the air-fuel mixture is formed is short and the injection destination is the combustion chamber.
For this reason, in a case of the air-fuel mixture formed inside the combustion chamber of the direct injection engine, a concentration difference occurs locally in fuel concentration, and thus the concentration difference in the fuel concentration often causes nitrogen oxide or an unburnt fuel component to be generated.
In particular, if the fuel directly injected into the combustion chamber reaches and adheres to combustion chamber wall surfaces such as a piston crown surface, a cylinder wall surface, and an engine head wall surface, or a valve, the fuel concentration locally becomes higher in the vicinity of the wall surface, thereby causing the unburnt fuel component (HC) to be generated. Otherwise, in a state of insufficient oxygen, the unburnt fuel component is degenerated into soot, thereby causing the soot to be discharged therefrom.
In order to cope with this problem, it is necessary to adjust a spray shape to fit an injection point, of the fuel and a shape of the combustion chamber so that the fuel spray is less likely to collide with the valve or the combustion chamber wall surfaces. Therefore, the spray shape of the direct injection gasoline engine needs to be very freely designed. In order to very freely design the spray shape, a multi-hole nozzle is advantageously employed which has multiple holes for forming the spray and which can set each injection direction of the holes to be oriented in a desired direction.
In addition, a factor of increasing the possibility that the fuel spray may adhere to the combustion chamber wall surfaces as described above includes a great penetrating force (penetration) of the fuel spray injected from the fuel injection valve. The spray of great penetration disadvantageously reaches a position far from the injection point within a short period of time. For this reason, in some cases, the spray of great penetration disadvantageously reaches and adheres to the combustion chamber wall surfaces before the fuel is sufficiently mixed with the air after the injection.
A method disclosed in PTL 1 is one of methods for coping with this problem. PTL 1 discloses a method for attenuating the penetration by decreasing the flow velocity of the fuel to be injected.